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WO1995016275A1 - Diodes polymeres conductrices a double fonction - Google Patents

Diodes polymeres conductrices a double fonction Download PDF

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Publication number
WO1995016275A1
WO1995016275A1 PCT/US1994/013999 US9413999W WO9516275A1 WO 1995016275 A1 WO1995016275 A1 WO 1995016275A1 US 9413999 W US9413999 W US 9413999W WO 9516275 A1 WO9516275 A1 WO 9516275A1
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WIPO (PCT)
Prior art keywords
layer
diode
light
reverse bias
conducting
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PCT/US1994/013999
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English (en)
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Alan J. Heeger
Gang Yu
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The Regents Of The University Of California
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Publication of WO1995016275A1 publication Critical patent/WO1995016275A1/fr

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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
    • H10K85/10—Organic polymers or oligomers
    • H10K85/111—Organic polymers or oligomers comprising aromatic, heteroaromatic, or aryl chains, e.g. polyaniline, polyphenylene or polyphenylene vinylene
    • H10K85/114—Poly-phenylenevinylene; Derivatives thereof
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K30/00—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation
    • H10K30/451—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation comprising a metal-semiconductor-metal [m-s-m] structure
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K50/00—Organic light-emitting devices
    • H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
    • H10K50/11—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K2102/00—Constructional details relating to the organic devices covered by this subclass
    • H10K2102/10—Transparent electrodes, e.g. using graphene
    • H10K2102/101—Transparent electrodes, e.g. using graphene comprising transparent conductive oxides [TCO]
    • H10K2102/103—Transparent electrodes, e.g. using graphene comprising transparent conductive oxides [TCO] comprising indium oxides, e.g. ITO
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K30/00—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation
    • H10K30/50—Photovoltaic [PV] devices
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
    • H10K85/10—Organic polymers or oligomers
    • H10K85/111—Organic polymers or oligomers comprising aromatic, heteroaromatic, or aryl chains, e.g. polyaniline, polyphenylene or polyphenylene vinylene
    • H10K85/113—Heteroaromatic compounds comprising sulfur or selene, e.g. polythiophene
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
    • H10K85/10—Organic polymers or oligomers
    • H10K85/141—Organic polymers or oligomers comprising aliphatic or olefinic chains, e.g. poly N-vinylcarbazol, PVC or PTFE
    • H10K85/143—Polyacetylene; Derivatives thereof
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/549—Organic PV cells

Definitions

  • This invention concerns diodes and their use and fabrication. More particularly, it concerns diodes which include semiconducting conjugated polymers. These diodes have both light-emission and photo-detection properties and may be used in displays and the like.
  • LEDs Solid-state light-emitting diodes
  • inorganic semiconductors such as gallium arsenide typically doped with aluminum, indium or phosphorus.
  • ITO indium/tin oxide
  • MEH-PPV poly (2 -methoxy-5 - (2 ' - ethylhexyloxy) -1, 4-phenylene vinylene)
  • MEH-PPV poly (2 -methoxy-5 - (2 ' - ethylhexyloxy) -1, 4-phenylene vinylene)
  • MEH-PPV poly (2 -methoxy-5 - (2 ' - ethylhexyloxy) -1, 4-phenylene vinylene
  • the DC sensitivity can be increased to typically about 9 x 10 "2 A/watt at an illumination of l ⁇ W/cm 2 . This corresponds to a quantum yield of more than 20% on an electron/photon basis.
  • This discovery that applying reverse bias can increase the photosensitivity of organic polymer- containing diodes can be embodied as a light-responsive diode system.
  • This system includes such a diode in combination with a source of a reverse-biasing voltage, a light source capable of impinging upon the diode, and a detector for detecting a current flow and/or a voltage produced by the diode as a result of the reverse biasing and the impinging of light upon the diode.
  • the diode includes three elements which are named using LED nomenclature.
  • the first is a layer of high work function material
  • the second is an active layer of semiconducting luminescent conjugated polymer in contact with the first layer
  • the third is a conductive metal layer preferably made up of or including at least one low work function material.
  • the above-described diode acts as a light-emitting diode.
  • the diode acts as a light-detecting photodiode.
  • diodes can be isolated devices or a plurality of them can be assembled into an array, which array can have the dual function of the individual diodes .
  • the dual function capability of the polymer diodes and arrays of such polymer diodes makes possible a variety of applications for this invention. By integrating the two functions of the polymer diode, electroluminescence and photo-detection response, in the same diode or in an array of diodes, one can achieve a display capable of performing a dual function -
  • Function 1 Input (by addressing or "writing” with a light stylus on the diode or the array) .
  • Function 2 Output (by electroluminescently displaying using the diode or the array) .
  • the present invention provides arrays of dual function diodes, said diode arrays consisting of individual pixels which are both light-emitting diodes and photo-detecting photodiodes, fabricated using semiconducting polymers as the active layer.
  • the present invention utilizes the processing advantages associated with the fabrication of said dual function polymer diode structures from soluble semiconducting (conjugated) polymers (and/or their precursor polymers) , cast from solution to enable the fabrication of large active areas.
  • Fig. 1 is a cross-sectional view of a diode of this invention assembled into a circuit so as to function in its forward biased or "light emitting" mode;
  • Fig. 2 is a cross-sectional view of the same diode as shown in Fig. 1 this time assembled into a circuit so as to function in its reverse biased or "photodetector" mode;
  • Fig. 3 is a graph of current-voltage characteristics taken from a device of the invention in the dark;
  • Fig. 4 is a graph showing the rectification ratio (R r ) for the same device
  • Fig. 5 is a graph of the current-voltage characteristic observed with the device in Fig. 3 in the dark (triangles) and illuminated with 2 mW/cm 2 (diamonds) , 6.3 mW/cm 2 (squares) , and 20 mW/cm 2 (dots) .
  • Fig. 6 is a graph of the photocurrent vs. bias voltage for several different incident light intensities applied to a device of this invention.
  • the solid curve is 20 mW/cm 2 ; dashed curve, 2 mW/cm 2 ; dot- dashed curve, 0.2 mW/cm 2 ; dotted curve, 20 ⁇ W/cm 2 ; and dash-triple dot curve, 2 ⁇ W/cm 2 ;
  • Fig. 7 is a graph of current density vs. incident light intensity for a device of this invention in which circles are short circuit current; open squares,
  • Fig. 8 is a graph of quantum yield vs. incident light intensity for a typical device of this invention in which circles are short circuit current; squares, at -4V; crossed squares, at -8V; and diagonal squares, at -10V.
  • the diodes are multilayer devices . These layers are referred to by the names typically used in light emitting diode descriptions. That is, they include: an "active layer” (layer 11) which is made up of the semiconducting luminescent conjugated organic polymer; a "hole-injecting layer” or “first layer” (layer 12) which, in a LED, functions as the positive electrode; and an "electron injecting layer", "rectifying contact” or “third layer” (layer 13) which serves as the negative contact in an LED.
  • the “hole injecting layer” is formed of a material having a “high work function.” A “high work function” is one above 4.5 eV.
  • the “electron injecting layer” is a conductive layer, typically a conductive metal layer, preferably formed of a material having a "low work function.”
  • a “low work function” is one below 4.3 eV.
  • the devices may also include an optional substrate or support 14.
  • This is a solid, rigid or flexible layer designed to provide robustness to the diodes.
  • the devices of this invention emit “light” under certain circumstances and provide an electrical response to “light” in other circumstances.
  • Light is defined broadly so as to include wavelengths beyond the visible range of 400-800 nm, that is so as to include ultraviolet of 200-400 nm and infrared of 800-2000 nm wavelengths .
  • the diode can serve as an "optical transformer” converting detected light of one wavelength into emitted light of another wavelength in the same pixel or element.
  • a device can be said to "emit” light when the quantity of light which it produces can be detected by the human eye or by an instrument .
  • transparent This term is used to refer to the property of a material of transmitting a substantial portion (i.e., at least
  • a “conductive” layer or material has a conductivity of at least 1 S/cm.
  • a “semiconductive” material has a conductivity of from 10 "12 S/cm to 10 "4 S/cm.
  • the relative size of values will be set in absolute value terms, such that a - 10 volt voltage is “larger” or “greater than” a -5 volt voltage.
  • the device 10 or 20 of this invention comprises a conductive metal contact 13, preferably fabricated of low work function metal on one side of a semiconductive conjugated polymer film 11.
  • a third layer, (high work function) electrode 12 is on the other side of the polymer film.
  • This electrode 11 is commonly transparent so that light 19 can pass to and from the active layer 11 as shown in Figs. 1 and 2.
  • these three layers can make up the device but more commonly a transparent substrate 14 is present adjacent to electrode 12.
  • Devices with inverted geometry are also useful. For example, by using an inorganic semiconductor such as silicon as the substrate 14 and by heavily doping this semiconductor to "conductive" metallic levels (as that term is defined herein) , the heavily doped semiconductor can serve both as the substrate and as the contact 13. In this inverted configuration, the active polymer layer 11 is applied next, and the transparent high work function electrode 12 is applied as the top layer.
  • Such inverted devices on inorganic semiconductor substrates offer the advantage of integrating the optical functions (light emission and light detection) with circuitry that can be built directly onto the inorganic semiconductor substrate .
  • Arrays of such dual-function polymer diodes can be fabricated by standard methods utilizing masks, lithography, silk-screening, etc. to achieve the necessary patterning. These methods are well known to those knowledgeable of the art of display technology.
  • the Active Layer is the Active Layer
  • the active layer in the diodes is semiconductive. It employs one or more conjugated luminescent polymers as its conductive element .
  • the active layer can be composed essentially completely of one or more conjugated polymers.
  • the active layer can be a blend of one or more conjugated polymers in hole- transporting or electron-transporting polymers.
  • the active layer can also be presented as a series of heterojunctions utilizing layers of semiconductive luminescent conjugated polymers as donors and organic polymeric acceptors having electronegativity in a range which will enable a photoinitiated charge separation process defined by the following steps: Step 1: D + A ⁇ 1,3 D * + A, (excitation on D) ; Step 2: 1,3 D * + A ⁇ 1,3 (D -- A)*, (excitation delocalized on D-A complex) ; Step 3: l ⁇ 3 (D -- A)* ⁇ 1 ' 3 (D ⁇ + -- A ⁇ " ) ⁇ (charge transfer initiated) ; Step 4: 1 - 3 (D ⁇ + -- A ⁇ ) * ⁇ 1 - 3 (D + * -- A "* ) , (ion radical pair formed) ;
  • Step 5 * -' 3 (D +# -- A " *) ⁇ D + * + A "* , (charge separation)
  • (D) denotes the donor semiconducting luminescent polymer and (A) denotes the accompanying organic polymeric acceptor; 1,3 denotes singlet or triplet excited states, respectively.
  • the heterojunction active layers are described more fully in United States Patent Application Serial Number 07/930,161, now United States Patent No. 5,331,183, which is incorporated herein by reference.
  • the other layers used herein preferably include at least one of the conjugated conductive polymers known in the art generally.
  • the conjugated polymers are soluble enough in some common solvent to form a casting solution so as to facilitate fabrication of the active layer in the device by casting or a like fluid phase process.
  • conjugated polymers examples include polyacetylene; polypyrrole; polyisothianaphene; poly(paraphenylene) ; poly(phenylenevinylene) or "PPV"; alkoxy derivatives of PPV, containing up to three, 1 to 10 carbon atoms long, alkoxys per PPV unit, and especially one to two, 1 to 8 carbon atoms long, alkoxys per PPV unit.
  • Such materials include, for example, poly(2-methoxy, 5- (2'ethylhexyloxy) -p-phenylenevinylene) (“MEH-PPV”) , poly(2, 5-dimethoxy-p-phenylenevinylene) (“PDMPV”) , and poly (2 , 5-bis (cholestanoxy) -1 , 4- phenylenevinylene) (“BCHA-PPV”) (see United States Patent Application Serial No. 07/800,555, now abandoned in favor of file-wrapper continuation Application Serial No.
  • MEH-PPV poly(2-methoxy, 5- (2'ethylhexyloxy) -p-phenylenevinylene)
  • PDMPV poly(2, 5-dimethoxy-p-phenylenevinylene)
  • BCHA-PPV poly (2 , 5-bis (cholestanoxy) -1 , 4- phenylenevinylene)
  • P3AT's polythiophene and poly(3-alkylthiophenes)
  • P3AT's polythiophene and poly(3-alkylthiophenes)
  • P3AT's polythiophene and poly(3-alkylthiophenes)
  • P3AT's polythiophene and poly(3-alkylthiophenes)
  • P3AT's polythiophene and poly(3-alkylthiophenes)
  • PANI polyquinoline and polyanilines
  • Representative PANI materials are described in United States Patent No. 5,196,144 which is incorporated by reference.
  • the MEH-PPV materials give good results and are presently preferred.
  • the conjugated polymer is present in admixture with one or more carrier polymers .
  • Carrier polymers may be added for cost savings or to improve durability or processability.
  • Carrier polymers are typically selected on the basis of compatibility of the conjugated polymer as well as with the solvent or solvents used in solvent processing, if that forming method is used.
  • blending of polar conducting polymers generally requires polar carrier polymers that are capable of co-dissolving with or absorbing polar materials.
  • polar carrier polymers include poly(vinyl alcohol) , poly(ethylene oxide) , poly(paraphenylene terephthalate) , poly (ethylene terephthalate) , poly(parabenzamide) , and the like.
  • nonpolar carrier polymers are typically selected.
  • the carrier polymer is optional.
  • the upper limit on carrier polymer proportions is dictated by the desire to not seriously interfere with the conductivity imparted by the conjugated polymer to the active layer.
  • the proportion of carrier polymer can range from 0 to about 90% of the total polymer in the active layer with proportions of 0 to 66% and especially 0 to 33% being preferred.
  • the film thickness optimally should be adjusted to an optical density such that light, such as visible light, is absorbed throughout the film thickness. Thicknesses from 600A to 2000A have been used in the experiments reported here .
  • the conjugated polymer active layer of the diodes of this invention is bounded on one surface by a conducting first layer.
  • This layer serves as a hole injector. When a substrate is present, this layer is typically between the substrate and the conjugated polymer layer.
  • This first layer is a conductive layer made of a high work function material.
  • This layer can be a film of an electronegative metal such as gold or silver, with gold being the preferred member of that group. It can also be formed of a conductive metal- metal oxide mixture such as indium-tin oxide (ITO) .
  • This layer can also be formed of a conductive polymer such as polyaniline (PANI) in the emeraldine salt form prepared using the counterion-induced processability technology disclosed in U.S. Patent No. 5,232,631 and in Applied Phys. Lett. 6 . 0:2711 (1992) or other suitable techniques.
  • PANI polyaniline
  • combinations of these layers may be used, for example a stock of alternating PANI and ITO layers.
  • This first layer should be conductive as evidenced by a sheet resistance of less than 300 ohms/square and preferably of less than 100 ohms/square.
  • the first layer should be transparent.
  • metal e.g., gold or silver
  • ultra thin layers such as below about 200A and especially from about 25 to about 100A.
  • metal oxides and the conjugated polymer material there is better transparency, and thickness of up to about 2000A, and especially 50 to 100A, can be employed.
  • These layers are commonly deposited by vacuum sputtering, (RF or magnetron) electron beam evaporation, thermal vapor deposition, chemical deposition and the like.
  • An electron-injecting contact is present on the other side of the conjugated polymer film.
  • This layer is fabricated from a conductive metal or metal alloy and preferably a low work function metal or alloy. Typical materials include aluminum, indium, calcium, barium and magnesium, with calcium being a particularly good material.
  • this contact can be a layer of conjugated polymer doped to metallic levels such as with one or more of the low work function metals just described.
  • These electrodes are applied by using methods well known to the art (e.g. vacuum evaporated, sputtered, or electron-beam evaporated) and act as the rectifying contact in the diode structure. These electrodes are from about 100 to about 20,000A thick with preferred thicknesses being from 500 to about 10,000A and especially 100 to 500A.
  • the conjugated polymer- based LEDs are prepared on a substrate.
  • the substrate should be nonconducting. It can be a rigid material such as a rigid plastic including rigid acrylates, carbonates, and the like, rigid inorganic oxides such as glass, quartz, sapphire, and the like. It can also be a flexible or rigid organic polymer such as polyester - for example poly(ethylene terephthalate) , flexible polycarbonate, poly(methylmethacrylate) , polystyrene and the like.
  • this substrate is not critical so long as it accomplishes its supporting function. Thicknesses of a few microns to a millimeter or more may be used.
  • the light impinging upon or emitted from the diode passes through the substrate.
  • the substrate should be transparent.
  • a key advantage offered by the present organic polymer-based diodes is the variety of processing methods which can be used to form them.
  • the diode In the more typical case of a substrated material, the diode is usually built up by adding layers serially. This normally takes the form of depositing the "first" layer on the substrate, followed by the active layer, followed by the low work function third layer.
  • the first layer can be laid down using any of the known thin-film forming processes, including evaporation, sputtering or the like. If a conjugated polymer first layer is employed, it may be put down by casting from a solution or suspension.
  • the conjugated polymer active layer can be deposited or cast directly from solution or suspension.
  • the solvent employed is one which will dissolve or disperse the conjugated polymer and optional carrier polymer and not interfere with their subsequent deposition.
  • organic solvents are used. These can include halohydrocarbons such as methylene chloride, chloroform, and carbon tetrachloride; aromatic hydrocarbons such as xylene, benzene, and toluene; other hydrocarbons such as decaline, and the like.
  • Mixed solvents can be used, as well.
  • Polar solvents such as water, acetone, acids and the like may be suitable. These are merely a representative exemplification and the solvent can be selected broadly from materials meeting the criteria set forth above.
  • the casting solution can be relatively dilute, such as from 0.1 to 20% w in concentration, especially 0.2 to 5% w. More concentrated materials can be used but may prove less desirable when forming the thin layers called for.
  • the first layer and high work function layer can be deposited upon a preformed active layer or the first layer and active layer can be formed upon a preformed second layer.
  • the diodes of this invention are bifunctional . They exhibit light 19 emission properties when driven with a forward bias as shown in Fig. 1.
  • power source 15 delivers a positive voltage to first layer 12 via line 16 and the circuit is completed by line 17 connected from the power source 15 to layer 13.
  • Typical emission turn-on voltages are plus 1.5 to 2 volts in many cases and with voltages from plus 1.5 to 10 volts being most useful.
  • power source 15' delivers a negative voltage to layer 12. The photocurrent is measured as a voltage drop on the load 18.
  • the photosensitivity increases with reverse voltage at least to -10 or -15 volts.
  • the reverse voltage can go to larger negative values as well .
  • Preferred reverse bias values range from about - 1.5 volts to about -20 volts and particularly from about -2.5 to about -15 volts. It will be noted that the figures presented herein show that a seemingly voltage and light-dependent current flow begins about immediately below the about plus 1.5 volt emission turn- on value. This suggests that in fact, it is possible to obtain a useful photovoltaic output at very low positive voltages (i.e., in the 0 to 1.5 volt range) . In view of the increased sensitivity at negative bias, this mode of operation is preferred.
  • the photoresponse increases significantly under reverse bias.
  • the DC sensitivity is 9xl0 ⁇ 2
  • A/watt under illumination of l ⁇ W/cm 2 corresponding to a quantum yield of more than 20% electrons/photon.
  • the same devices exhibit electroluminescence under forward bias. Electroluminescence becomes detectable in forward bias for voltages greater than 2.0 volts and visible under room light for currents larger than 10 "3 A/cm 2 . The emitted light is proportional to the forward current with external quantum efficiency of approximately 1% photons/electron for voltages above about 2.5 volts.
  • the polymer diode is a dual-function device capable of being used in display technology for both input
  • the present invention also provides arrays of dual-function diodes, said diode arrays consisting of individual pixels which are both light-emitting diodes and photo-detecting photodiodes, fabricated using semiconducting polymers as the active layer.
  • the present invention also permits one to utilize the processing advantages associated with the fabrication of dual function polymer diode structures from soluble semiconducting (conjugated) polymers
  • the conjugated polymer is highly colored (bright red-orange) .
  • the precursor polymer was converted to the conjugated MEH-PPV by heating to reflux (approx. 214°C) in 1, 2 , 4-trichlorobenzene solvent.
  • the product was identical with the material obtained in the first preparation.
  • Dual function devices were fabricated by evaporating a metal (Ca) contact on the front of a MEH-PPV film (thickness on the order of 1000A) which was deposited from solution onto a glass substrate, said substrate being partially coated with a layer of indium- tin-oxide (ITO) .
  • the active area of each device was 0.1 cm 2 .
  • the MEH-PPV was purchased from UNIAX Corporation. Further details on the synthesis of MEH-PPV can be found in literature (F. Wudl, P.M. Allemand, G. Srdanov, Z. Ni, and D. McBranch, in Materials for Nonlinear Optics : Chemical Perspectives, Ed. S.R. Marder, J.E. Sohn and G.D.
  • MEH-PPV films were spin-cast from a 0.5% solution in xylene at a spin speed of 2000 rpm. Typical film thicknesses are approximately 1000A, corresponding to an optical density of approximately 0.6 at the absorption peak. Devices with polymer film thicknesses from 600A to 2000A have also been fabricated and tested
  • the Ca electrode was vacuum evaporated onto the top surface of the MEH-PPV with a thickness of approximately 5000A. Electrical data were obtained with a Keithley
  • Source-Measure Unit For the photodiode (and photovoltaic) measurements, light was incident from the ITO side.
  • the excitation source was a tungsten-halogen lamp filtered with a bandpass filter (center wavelength of 430 nm, bandwidth of 100 nm) and collimated to form a homogeneous 5mm x 10mm area of illumination.
  • the maximum optical power at the sample is 20 mW/cm 2 as measured by a calibrated power meter.
  • a set of neutral density filters were used for measurements of intensity dependence.
  • the emitted light is proportional to the forward current with external quantum efficiency of approximately 1% photons/electron for V > 2.5 V, similar to that reported earlier for such Ca/MEH-PPV/ITO devices.
  • a photovoltaic effect is also expected for this device. This, in fact, is observed as shown in Fig. 5, where the I-V dependencies are plotted (linear scales) for the device in the dark and under illumination at 2, 6.3 and 20 mW/cm 2 .
  • the open circuit voltage saturates at 1.6 V and the short circuit current is 6.1 ⁇ A/cm 2 .
  • the energy conversion efficiency is about 0.02%, similar to that observed in PPV devices (S. Karg, W. Riess, V. Dyakonov and M. Schwoerer, Synth. Metals 54, 427 (1993) ; H. Antoniadis, B.R. Hsieh M.A. Abkowitz, S.A. Jenekhe and M. Stolka, Synth. Metals (in press) ; R. Friend, Oral presentation at the Minisymposium on Polymer Light Emitting Diodes, Eindhoven, Sept. 15-17, 1993) .
  • the corresponding quantum yield at zero bias is 8.8x10 4 electrons/photon (el/ph) .
  • the Ca/MEH-PPV/lTO device operates as a photo-diode.
  • the reverse current (with no illumination) remains nearly constant at -10 "11 A/cm 2 for voltages less than 2.5 V.
  • the current begins to increase exponentially.
  • the photosensitivity increases significantly under reverse bias.
  • the photocurrent at -2 V is 19 ⁇ A/cm 2 , five orders of magnitude higher than the dark current at the same voltage.
  • polymer diode device operates as a photo-diode capable of sensitive and relatively low noise photo-detection of incident light under conditions of reverse bias.
  • This example when combined with Example 2, demonstrates the dual-function capability of the polymer diode.
  • the photocurrent obtained from a Ca/MEH-PPV/ITO diode device operated as a photo-diode is plotted as a function of bias voltage for several light intensities.
  • the photocurrent of the Ca/MEH-PPV/ITO device increases exponentially with the reverse bias.
  • the current density reaches 0.33 mA/cm 2 under 20 mW/cm 2 .
  • the photosensitivity is 1.6xl0 ⁇ 2 A/W, corresponding to a quantum yield of 4.8 % ph/el .
  • these numbers increase to 0.045 A/W and 13% ph/el, respectively.
  • the photo-response increases nearly linearly with light intensity ( ⁇ I 0 - 95 ) over the entire range measured, i.e. over more than 5 orders of magnitude.
  • No signature of saturation is observed at 20 mW/cm 2 (the highest light intensity in the measurement) .
  • Fig. 7 in which the short circuit current and the photocurrent under reverse bias (at -4V and at -8V) are plotted.
  • the corresponding quantum yields are plotted in Fig. 8. Due to the slight sublinearity of the intensity dependence, the quantum yields are even higher at low light intensities. For example, at -10V, the quantum yield is >20% (electron/photon) under illumination with 1 ⁇ W/cm 2 .
  • Example 5 demonstrates that the polymer diode device operates as a photo-diode capable of relatively efficient photo-detection of incident light under conditions of reverse bias. This example, when combined with Example 2, demonstrates the dual-function capability of the polymer diode.
  • Example 5 when combined with Example 2, demonstrates the dual-function capability of the polymer diode.
  • Example 6 The photo-response was measured for similar devices fabricated with both aluminum and indium as the electron injecting contacts; contact, e.g. A1/MEH-PPV/ITO.
  • the V oc and I sc under 20 mW/cm 2 are 1.05 V and 1.1 ⁇ A/cm 2 , respectively, and the sensitivity and the quantum yield at -10V are 5xlO "3 A/W and 1.4% el/ph.

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  • Led Devices (AREA)

Abstract

L'invention se rapporte à des diodes à double fonction comportant trois couches actives conjuguées de polymères organiques. Un tel dispositif comprend, sur un côté d'un film polymère conjugué semi-conducteur (11), un contact (13) métallique conducteur, de préférence fabriqué dans un métal fonctionnant à une faible intensité. La troisième couche formant une électrode (12) est située sur l'autre côté du film polymère. Cette électrode est généralement transparente de manière que la lumière (19) puisse aller vers la couche active (11) ou venir de celle-ci. Ces trois couches peuvent constituer le dispositif, mais plus généralement, on place un substrat transparent (14) contre l'électrode (12). Lorsqu'on polarise ces diodes de façon positive, elles fonctionnent comme des émetteurs de lumière, et lorsqu'on les polarise de façon négative, elles agissent comme des photodiodes hautement efficaces. L'invention se rapporte également à des procédés de préparation et d'utilisation de ces diodes dans des affichages ainsi qu'à des dispositifs d'entrée/sortie.
PCT/US1994/013999 1993-12-07 1994-12-06 Diodes polymeres conductrices a double fonction WO1995016275A1 (fr)

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US08/163,174 US5504323A (en) 1993-12-07 1993-12-07 Dual function conducting polymer diodes
US08/163,174 1993-12-07

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